A light-emitting diode (LED) is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction. LEDs have unique advantages over other lighting solutions. They operate at a high efficiency to produce more light output with lower input power, and have an inherently longer service life. For example, LEDs typically produce more light per watt than incandescent bulbs, and last much longer. Also, the output light of LEDs can be color matched and tuned to meet stringent lighting application requirements. In contrast, the output light of incandescent bulbs and fluorescent lights can not be as effectively tuned. Thus, LEDs which are often used in battery powered or energy saving devices are becoming increasingly popular in higher power applications such as, for example, flashlights, area lighting, and regular household light sources.
Unlike incandescent bulbs and fluorescent lights, LEDs are semiconductor devices that conventionally must operate at lower temperatures. This is so because, in part, the LED p-n junction temperature needs to be kept low enough to prevent degradation and failure. While incandescent bulbs and fluorescent lights lose heat by direct radiation from a very hot filament or gas discharge tube, respectively, LEDs must remove heat by conduction from the p-n junction to the case of the LED package before being dissipated. Conventional LED packages thus typically employ various heat removal schemes. The effectiveness of the heat removal scheme determines how well such LEDs perform, as cooler running temperatures yield higher efficacy for a given level of light output.
One conventional passive approach to cooling LEDs provides a finned heat sink exposed to external air. In such an approach, the thermal choke point in the heat transfer equation is typically the heat sink to air interface. To maximize heat transfer across this interface, the exposed heat sink surface area is typically maximized, and the heat sink fins are typically oriented to take advantage of any existing air flow over the fins. Unfortunately, such a conventional passive approach does not effectively cool LEDs for various reasons. Thus, in typical LED lighting applications that utilize this approach, the LEDs are often operated at less than half of their available light output capacity, to extend their lifetime and to preserve their efficiency.
Other LED lighting applications utilize a conventional active approach to cooling LEDs that forces air over a finned heat sink with, for example, a powered fan. Another example is a patent pending product, referred to as “SynJet,” which uses a diaphragm displacement method to “puff” air over a finned heat sink. While such active approaches may be more effective in removing heat from LEDs, they have many negative issues. For example, these approaches typically utilized powered components which add cost to a given LED lighting application. In addition, these approaches typically are noisy, typically exhibit parasitic electrical loss, and typically introduce unreliable moving parts.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.